1. Field of the Invention
The present invention relates to a storage device, a head returning method, and a head returning apparatus, and, more specifically to a storage device, a head returning method, and a head returning apparatus that can return a head safely, when the head is retracted.
2. Description of the Related Art
A magnetic disk drive such as a hard disk drive (HDD) is used mainly as an auxiliary storage of a computer, and used for a dedicated device for business use, which requires a large capacity of random access recording. In recent years, with the digitalization of household appliances, there is a new application of recording audio and image data as digital data, and use thereof in general household products is increasing (for example, a hard disk video recorder, a portable music player, and the like).
When the magnetic disk drive has a strong shock such as a fall, the head can collide on a disk surface to damage the disk, and read and write of data may not be possible. Particularly, since a fall during an operation of the magnetic disk drive is likely to cause a failure, when handling a product having a magnetic disk drive built therein for portable use, it is necessary to take care so as not to cause a strong impact thereon.
To cover such a defect, there is a technique for automatically retracting the head of the hard disk drive when a sensor provided therein detects a fall (see Japanese Patent Application Laid-open No. 2002-208239).
When the head is retracted by such a technique, the head needs to be returned after appropriately determining that the hard disk drive is not in a falling state any more. However, if the head is simply returned after a predetermined time has passed since the head is retracted, the head can collide on the disk surface in a state that, for example, the hard disk drive is rolling.
Therefore, there is another technique that after a head is retracted, when a sensor detects that acceleration applied to a hard disk drive becomes zero, the head is returned (see, for example, Japanese Patent Application Laid-open No. 2004-199743). According to this technique, when the head is retracted during disk access, the contents of the disk access failed due to retraction of the head are stored, and the disk access is resumed after returning the head.
However, as in the above conventional technique in the method of returning the head when the sensor detects that acceleration applied to the hard disk drive becomes zero, if the way of falling of the magnetic disk drive is complicated, there is a possibility that the head is returned even the magnetic disk drive is still rolling.
Specifically, after the magnetic disk drive falls from a desk, when the magnetic disk drive collides on a chair and falls again, and finally collides on the floor, the acceleration of the magnetic disk drive changes in a complicated manner, and the acceleration can become zero momentarily, during the fall. In this case, if the head is returned during the fall, it can collide on the disk surface due to the impact applied to the magnetic disk drive thereafter.